Generally, an ink jet head of one type has an actuator including a diaphragm and a plurality of piezoelectric elements to eject ink from a plurality of pressure chambers. In such an ink jet head, the diaphragm is deformed by a piezoelectric element to pressurize ink inside a corresponding pressure chamber, and then the ink is ejected.
Depending on a method to form the actuator, especially when using photolithography, compressive stress may remain in the diaphragm of the actuator.
When the compressive stress in the diaphragm is excessively great, upon driving of the actuator, the actuator may undergo buckling distortion due to the compressive stress of the diaphragm. When there is variation in the compressive stress of the diaphragms among the plurality of actuators, the degree of buckling distortion may differ among the actuators, which lead to uneven deformation characteristics among the actuators. As a result, the ink ejection characteristics may become uneven. Also, durability of the actuators may decrease due to the buckling distortion.